The field of the invention is ozonolysis and the present invention is particularly concerned with the reaction of olefins with ozone in a carboxylic acid medium.
The state of the art of ozonolysis may be ascertained by reference to the Kirk-Othmer, Encyclopedia of Chemical Technology, 2nd Edition, Vol. 8 (1966) pp. 821-822 and Vol. 14 (1967) under the section OZONE, pp. 410-432, particularly pp. 418-420 where ozonides and ozonide reactions are disclosed, p. 430 where the ozonolysis of oleic acid is disclosed, pp. 421-427 where ozone generation is disclosed, and U.S. Pat. Nos. 2,813,113 and 2,804,473, the disclosures of which are incorporated herein.
The reaction of olefins with ozone (ozonolysis) is known as disclosed in Kirk-Othmer, Vol. 14, pp. 418-419, ibid. In addition to its significance regarding manufacture and analysis, ozonolysis is becoming increasingly important in the chemical industry as a synthetic process. Both linear hydrocarbons and cyclic hydrocarbons with one or more double bonds are suitable as input olefins. For economic reasons, the use of relatively expensive ozone especially for the higher olefins is of interest only for a relatively low specific consumption of ozone per unit mass of the olefin and for a high degree of added value of the end product(s).
Depending on the process, ozonolysis results in peroxidic, aldehydic and/or carboxylic-acidic sequential products or their derivatives (P. S. BAILEY, Chem. Rev. 58, 925, 1958).
As a rule the industrial process does not stop at the stage of the peroxidic ozonolysis products, rather these intermediate products are subjected to a post-treatment in order to obtain stable reaction products. Since the ozonides and di- or oligomeric peroxides most often cannot be converted simply, and then only with a moderate yield into stable end products, the ozonolysis reaction is carried out in so-called participating solvents such as alcohols and carboxylic acids when further reaction of the ozonolysis products is intended. Carboxylic acids are the especially preferred solvents and contrary to the alcohols, they are not attacked by ozone in an oxidizing manner. By further suitably processing by thermolysis, reduction or oxidizing thermolysis the reaction products contained in such solvents, aldehydes, aldehyde/carboxylic-acid mixtures of carboxylic acids are obtained. When cyclic olefins are used, dialdehydes, aldehyde carboxylic acids or dicarboxylic acids are obtained.
Besides air, pure oxygen and mixtures or gases containing oxygen are applicable as the input gas for ozone production. However, even when pure oxygen is used which offers economic advantages over air and mixtures of gases containing oxygen, as much as and more than 90% by volume of the gas used for ozone production remains unutilized. Accordingly, where relatively costly input gases are involved, such as oxygen, oxygen-rich gas mixtures and oxygen-enriched air, there is a problem of economically making use of the practically ozone-free residual gas after the ozonolysis reaction. It is the exception that the residual gas from the ozonolysis is used without further purification for another production run. Even when this is the case, all the shortcomings of two mutually coupled processes arise. Therefore, the preferable approach for utilizing the residual gas is to feed it back, following a pertinent purification, into the ozone production.
Gas purification using electrostatic separation as known from the process of U.S. Pat. No. 2,813,113 is not a generally satisfactory solution. The voltages at which such an apparatus is operated may result in arc formation on account of electric breakdown and hence the oxygenated gas laden with organic substances may ignite. Furthermore, the moisture from humidity introduced with the gas into purification apparatus additionally affects the operational reliability of the electrostatic separators.